Conventional read only memories include a network of elementary memory cells (or memory points) arranged in lines (or rows) and columns. All the memory cells in a line are activated by a first metallization or connection (i.e., a word line), while all the cells in a column can be read based on the voltage across the terminals of a column's connection or bit lines. That is, the activation of a word line and the measurement of the voltage across the terminals of a bit line make it possible to read the content of the memory cell situated at the intersection of the word line and the bit line. The value of the information stored depends on the level (high or low) of the voltage on the bit line. Accordingly, with a conventional read only memory cell it is only possible to code or store a digital word of one bit (which can be zero or one).